1. Field of the Invention
The present invention relates to a transceiver circuit for driving a signal-outputting power transistor that is connected between a communication line and a ground.
2. Description of the Related Art
JP 2004-289597A2 or its counterpart U.S. Patent application U.S. 2004/0141560A1 discloses an integrated circuit for a vehicle network transceiver that includes a transceiver IC 10, in which an output transistor 1 is mounted, as shown in FIG. 6. The output transistor 1 is supplied with a driving signal of a trapezoidal wave-form to output a signal to a communication line 3 in order to suppress noises that are generated due to an abrupt signal change. The communication line 3 is connected with an outside control circuit 2 and with a receiving side power supply line via a series circuit of a resistor 4 and a diode 5. The output transistor 1 is always biased by a constant current circuit 9 to output a low level signal at an input/output terminal 7 when the level of a transmission signal is low. When the level of the transmission signal is high, the trapezoidal signal is applied to the base of the transistor 1 to output a high level signal. Therefore, the output transistor 1 is still active and turned on.
In case the vehicle network transceiver has a common communication line 3 for both signal transmitting and signal receiving, it is not possible to suppress the noise if a noise gets into the output transistor 1 via a receiving side power line 6 and the series circuit of the resistor 4 and the diode 5. Further, the disclosed transceiver IC 10 can not control voltage fluctuation of a power supply line in the case that the transceiver IC 10 is mounted in a vehicle alternator or the like that generates ripple voltage.